Amanitaceae

Berch, Shannon M., Witte, Thomas E. & Tanney, Joey B., 2023, Preliminary assessment of the ectomycorrhizal fungi of Quercus garryana on Vancouver Island, British Columbia, Canada, Botany 101 (6), pp. 424-448 : 442

Amanitaceae

The death cap mushroom, A. phalloides , was co-introduced with its ornamental tree hosts from Europe to both the North American west coast and eastern United States. The western range extends from southern California to Vancouver, BC, with the first collections in California dating back to the late 1930s. Some contemporary ECM communities in California are apparently dominated by A. phalloides ( Wolfe et al. 2010) . Since the first Canadian record from Lake Errock, BC in 1997, A. phalloides has been detected throughout the Lower Mainland and Vancouver Island on ornamental hosts (e.g., Betula pendula Roth , Carpinus betulus L., F. sylvatica ) and recently from an urban-interface Garry oak stand ( Berch et al. 2017).

The invasion of North American ecosystems by A. phalloides is an example of mutualist spillover, whereby a mutualist of an introduced or invasive plant jumps to native plant hosts ( Dickie et al. 2017). Most attention on biological invasions focuses on pathogens; however, introducing mycorrhizal fungi and other mutualists can also have detrimental effects. Amanita phalloides invasions are particularly concerning because the consumption of its exceptionally toxic mushrooms is responsible for 90% of the world’s mushroomassociated fatalities ( Moor-Smith et al. 2019). On Vancouver Island, one death and several poisoning cases are associated with consumption of A. phalloides mushrooms. Its successful establishment and expansion in natural forests is also concerning because of possible ecological effects. For example, ECM invasions can reduce ECM biodiversity (e.g., through resource competition) and facilitate invasions by non-native tree species (i.e., increase ecosystem invasibility) ( Dickie et al. 2010). ECM invasions via the live plant trade are therefore of phytosanitary concern, especially when they involve generalist species with toxic sporocarps.

Amanita phalloides was recently found in a natural stand of Garry oak on one of the Gulf Islands off Vancouver Island (Berch and Tanney, pers. comm.). The impending, or possibly ensuing, invasion of natural Garry oak stands by A. phalloides emphasizes the need to survey ECM communities, and the general mycobiota, of Garry oak in its most northern range. Benchmark biodiversity data are needed for threatened Garry oak meadow ecosystems, especially for pre-invasion belowground ecosystems.